The receptor for the alpha-factor mating pheromones of the yeast, Saccharomyces cerevisiae, has sequence homology to the family of seven-transmembrane domain G-protein coupled receptors. The three-dimensional structure of bacteriorhodopsin and the hydropathy analysis of sequence of the alpha-factor receptor were combined to predict the organization of the seven membrane spanning helical domains and the intervening extra and intra cellular connecting regions. Structural analysis of the alpha-factor receptor have been limited to conformational studies of the fragments of the transmembrane domain 6 (TM6), the transmembrane domain 7 (TM7) and the three extracellular domains, E2, E3 and E4. The CD studies of the TM6 and TM7 domains of the alpha-factor receptor confirm the predicted ?-helical secondary structure of the transmembrane domains in micelles. Solid state NMR studies of the TM6 domain confirm the helical structure as well as determined the overall orientation of the helix in the lipid bilayer. Selectively 15N labeled peptide sequences were synthesized and incorporated into lipid bilayers oriented on glass plates. Measurements of the 15N chemical shift anisotropy and the 15N-1H dipolar couplings for the individual sites produce a set of constraints on the structure of the peptide. The peptide was determined to fit an alpha-helical confirmation at the carboxyl terminal region of the peptide, the amino terminal segment forms a turn confirmation. The helix axis is parallel to the bilayer normal.